Tailoring coercivity of unbiased exchange-coupled ferromagnet/antiferromagnet bilayers

This paper reports experimental results obtained on unconventional exchange-coupled ferromagnet/antiferromagnet (FM/AF) system showing zero net bias. The Curie temperature of the FM (NiCu) is lower than the blocking temperature of the AF (IrMn). Samples were either annealed or irradiated with He, Ar, or Ge ions at 40 keV. Due to the exchange coupling at the FM/AF interface, the coercivity (H-C) of the as-deposited FM/AF bilayer is rather higher than that of the corresponding FM single layer. We found that by choosing a proper ion fluence or annealing temperature, it is possible to controllably vary H-C. Ion irradiation of the FM single layer has lead to only a decrease of H-C and annealing or He ion irradiation has not caused important changes at the FM/AF interface; nevertheless, a twofold increase of H-C was obtained after these treatments. Even more significant enhancement of H-C was attained after Ge ion irradiation and attributed to ion-implantation-induced modification of only the FM layer; damages of the FM/AF interface, on the other hand, decrease the coercivity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731717]